This application relates to a scroll compressor wherein valves are selectively actuated based upon adverse conditions in a scroll compressor to change the back pressure chamber tapped fluid.
Scroll compressors are becoming widely utilized in refrigerant compression applications. In a scroll compressor a first scroll member includes a base with a generally spiral wrap extending from its base. A second scroll member has a base with a generally spiral wrap extending from its base. The wraps of the two scroll members interfit to define compression chambers. The second scroll member is caused to orbit relative to the first scroll member, and as the two wraps orbit relative to each other an entrapped refrigerant is compressed. Scroll compressors are widely utilized due to efficiency and other advantages. However, they also raise challenges to a scroll compressor designer. One challenge relates to resisting a so-called xe2x80x9cseparating forcexe2x80x9d. As the refrigerant is compressed between the two relatively orbiting scroll members, a force is created by the compressed refrigerant tending to separate the two scroll members. To resist this force, compressed refrigerant is tapped to a back pressure chamber behind one of the two scroll member bases. This back pressure force resists the separating force and holds the two scroll members in contact with each other.
There are challenges with regard to providing an optimum back pressure chamber force. The back pressure chamber force which is optimum will vary with varying conditions within the compressor. There are situations wherein the compressor will be operating under adverse conditions, and it is difficult to address those conditions while at the same time providing a desirable back pressure force for normal operating conditions.
As an example, scroll compressors may sometimes operate at a high pressure ratio condition. If there is a loss of charge or an indoor fan failure, then very high pressure ratio conditions can be created. The stability of the scroll compressor is effected by the back pressure chamber force. A desired back pressure chamber force to obtain optimum stability increases as the pressure ratio increases. Thus, a desirable back pressure chamber to obtain optimum stability at normal operating ranges would be undesirably low at high pressure ratio operation.
It is thus desirable to provide a scroll compressor having a condition responsive control of the pressure in a back pressure chamber.
In the disclosed embodiment of this invention, a back pressure tap from an intermediate pressure chamber delivers an intermediate pressure fluid to a back pressure chamber in a scroll compressor. A second selective tap communicates discharge pressure chamber to the back pressure chamber. A valve is biased to close this second tap. The valve is conditioned responsive, such that if conditions within the scroll compressor indicate a higher pressure would be desirable within the back pressure chamber, the valve moves to an open position and discharge pressure refrigerant is delivered to the back pressure chamber. In one preferred embodiment, a bi-metal snap valve is utilized which is normally biased to close the second discharge pressure tap, but is movable to a position at which it allows flow from the second discharge pressure tap into the back pressure chamber when an elevated temperature is experienced in the scroll compressor.
In another embodiment, it is the intermediate pressure tap which is closed by a valve upon certain conditions. In this embodiment, the valve is normally open and allows flow into the back pressure chamber under normal conditions. However, if an elevated temperature is reached, then the valve is moved to a position at which it will block flow of at least intermediate pressure fluid to the back pressure chamber. In one embodiment, this valve will block the flow of any refrigerant into the back pressure chamber. In such condition, the back pressure chamber will quickly move to a suction pressure and the two scroll members will move out of contact with each other. This will eliminate any resultant damage which may otherwise be experienced if the scroll compressor was operated at a high pressure ratio condition. In a third embodiment the valve which selectively closes off the intermediate pressure tap only will close portions of the tap at a lower pressure range. The tap will be free to deliver refrigerant into the back pressure chamber through a portion of the orbiting cycle of the orbiting scroll associated with higher pressure refrigerant.
In sum, the present invention provides a scroll compressor wherein the pressure of refrigerant delivered to a back pressure chamber is controlled by a condition responsive valve. The invention thus allows a scroll compressor designer to ensure safe operation of the scroll compressor at a variety of extreme conditions, and across a variety of otherwise undesirable operating conditions.